The prior art recognizes the desirability of incorporating dyes into polymerizable (meth)acrylate compositions, used as adhesives, sealants and coatings, to indicate cure. For example, Wojciak U.S. Pat. No. 6,890,399 discloses the use of anthraquinone and/or xanthene dyes for that purpose in such compositions. However, dyes taught by Wojciak exhibit an inherent photobleaching property (i.e., they lose color merely upon irradiation, even in the absence of photoinitiators), and do not therefore provide a reliable indication that curing of the composition has actually occurred; they show only that the composition has been exposed to a wavelength of radiation to which the dye itself responds by changing color.
Moreover, dyes disclosed by Wojciak do not undergo irreversible reaction under the curing conditions utilized, and therefore do not exhibit a permanent color change. The tendency for an original color to redevelop constitutes a serious drawback because, in many instances (e.g., in the fabrication of medical devices), it is imperative that assurance can be given, and can be demonstrated to the purchaser or consumer, that an adhesive employed has been fully cured and that harmful (e.g., cytotoxic) ingredients have been consumed; color redevelopment may be undersirable from aesthetic standpoints as well.